This research proposal is designed to capitalize on recent advances of knowledge of immunoglobulin structure. This should allow better definition of immunoglobulin regulation, specific biological functions and hopefully, genetic regulation. The specific aims of this proposal are the following: 1. Completion of the total primary structure of J-chain. 2. Definition of disulfide linkages in J-chain and determination of sites of J-H linkages. 3. Examination of molecular parameters necessary for the C micron 4 domain of IgM to activate Cl. 4. Examination of the structure of the membrane component of mouse lymphocyte (TL) as a possible primoidial immunoglobulin-like molecule. It is anticipated that these studies will lead to new insights into the struture and function relationships of immunoglobulin molecules. We further anticipate that this knowlodge can be adapted for pharmacodynamic application to therapy and management of inflammatory diseases of deficiency in function of the immune system.